120
Y. Li et al.
high conductivity, and due to the presence of oxygen vacancies, Ti n O 2n−1 has the
characteristics of under-d electrons and can interact with Pt with super-d electron
characteristics. This electronic interaction between Ti n O 2n−1 and Pt can promote
ORR activity of Pt [209, 210].
4.3.2 Transition Metal Carbides ORR Co-Catalyst
In 2005, based on the previously discovered tungsten oxide (WO 3 ) synergistically
enhanced Pt-based electrocatalyst [211], P.K. Shen et al. first discovered the enhanced
effect of tungsten carbide on Pt ORR activity [212, 213]: Under the “synergistic
effect” of tungsten carbide, the ORR on-set potential of Pt has a significant positive
shift, and when it gets the same performance as Pt/C, it can reduce the amount of
Pt by 2/3. Moreover, the tungsten carbide is more stable than tungsten oxide. This
work has attracted widespread attention at home and abroad, and researchers have
invested in this field in anticipation of the development of more excellent Pt-based
ORR catalysts [139, 204–216]. Hsu et al. [217] deposited different number of layers
of Pt atomic layer on the surface of WC by atomic layer deposition method. They
found that in 0.5 M H 2 SO 4 medium, only 20 Atomic layer thickness of Pt deposit
on the surface of WC, its ORR performance is equivalent to ordinary Pt catalyst.
Because the synthesis temperature of WC is relatively high, the particles of WC
prepared earlier are relatively large and the specific surface area is relatively small. To
maximize the synergistic effect of WC, it is necessary to synthesize WC with small
particles and large specific surface area. Yan et al. [218] used an ion exchange resin
to exchange the precursors of W and Fe, and found a new way to synthesize WC,
which greatly reduced the synthesis temperature, and obtained WC nanoparticles
smaller than 2 nm, which is the smallest WC nanoparticles currently synthesized.
Its ORR mass activity at 0.9 V (vs. RHE) reached 257.7 mA mg
−1
Pt , which is more
than twice the commercial Pt/C (124.6 mA mg
−1
Pt ). Wang et al. [219] first prepared
microspheres using ammonium metatungstate and glucose as precursors, and then
heat-treated at 950 °C to obtain tungsten carbide microspheres (TCMSs). Its specific
surface area reached 256 m
2 g
−1 . After compounding with Pt, the ORR activity of
Pt/TCMSs was increased by 200% compared with commercial Pt/C.
They further performed stability tests on Pt-WC THP /G. After 6,000 cyclic voltammetry tests, the ECSA of the commercial Pt/C catalyst after the end of the stability
test was reduced to 42.4%, while the ECSA of Pt-WC THP /G still remained 89.2%.
After 6,000 cycles of cyclic voltammetry stability tests, the Pt-WC THP /G catalyst’s
half-wave potential for oxygen reduction was only 7 mV lower than the initial, while
the half-wave potential of commercial Pt/C negatively shift 36 mV. The mass activity
of the Pt-WCTHP/G catalyst still reached 480 mA mg
−1
Pt (0.9 V vs. REH) after the
stability test, which is more than 8 times the mass specific activity of commercial
Pt/C (56 mA mg
−1
Pt ) after the stability test, as shown in Fig. 4.24.
In order to uncover the mechanism of WC’s activity enhancement for Pt-based
ORR catalysts, Professor P.K. Shen et al. [220] used the Gaussian 03 program to
Y. Li et al.
high conductivity, and due to the presence of oxygen vacancies, Ti n O 2n−1 has the
characteristics of under-d electrons and can interact with Pt with super-d electron
characteristics. This electronic interaction between Ti n O 2n−1 and Pt can promote
ORR activity of Pt [209, 210].
4.3.2 Transition Metal Carbides ORR Co-Catalyst
In 2005, based on the previously discovered tungsten oxide (WO 3 ) synergistically
enhanced Pt-based electrocatalyst [211], P.K. Shen et al. first discovered the enhanced
effect of tungsten carbide on Pt ORR activity [212, 213]: Under the “synergistic
effect” of tungsten carbide, the ORR on-set potential of Pt has a significant positive
shift, and when it gets the same performance as Pt/C, it can reduce the amount of
Pt by 2/3. Moreover, the tungsten carbide is more stable than tungsten oxide. This
work has attracted widespread attention at home and abroad, and researchers have
invested in this field in anticipation of the development of more excellent Pt-based
ORR catalysts [139, 204–216]. Hsu et al. [217] deposited different number of layers
of Pt atomic layer on the surface of WC by atomic layer deposition method. They
found that in 0.5 M H 2 SO 4 medium, only 20 Atomic layer thickness of Pt deposit
on the surface of WC, its ORR performance is equivalent to ordinary Pt catalyst.
Because the synthesis temperature of WC is relatively high, the particles of WC
prepared earlier are relatively large and the specific surface area is relatively small. To
maximize the synergistic effect of WC, it is necessary to synthesize WC with small
particles and large specific surface area. Yan et al. [218] used an ion exchange resin
to exchange the precursors of W and Fe, and found a new way to synthesize WC,
which greatly reduced the synthesis temperature, and obtained WC nanoparticles
smaller than 2 nm, which is the smallest WC nanoparticles currently synthesized.
Its ORR mass activity at 0.9 V (vs. RHE) reached 257.7 mA mg
−1
Pt , which is more
than twice the commercial Pt/C (124.6 mA mg
−1
Pt ). Wang et al. [219] first prepared
microspheres using ammonium metatungstate and glucose as precursors, and then
heat-treated at 950 °C to obtain tungsten carbide microspheres (TCMSs). Its specific
surface area reached 256 m
2 g
−1 . After compounding with Pt, the ORR activity of
Pt/TCMSs was increased by 200% compared with commercial Pt/C.
They further performed stability tests on Pt-WC THP /G. After 6,000 cyclic voltammetry tests, the ECSA of the commercial Pt/C catalyst after the end of the stability
test was reduced to 42.4%, while the ECSA of Pt-WC THP /G still remained 89.2%.
After 6,000 cycles of cyclic voltammetry stability tests, the Pt-WC THP /G catalyst’s
half-wave potential for oxygen reduction was only 7 mV lower than the initial, while
the half-wave potential of commercial Pt/C negatively shift 36 mV. The mass activity
of the Pt-WCTHP/G catalyst still reached 480 mA mg
−1
Pt (0.9 V vs. REH) after the
stability test, which is more than 8 times the mass specific activity of commercial
Pt/C (56 mA mg
−1
Pt ) after the stability test, as shown in Fig. 4.24.
In order to uncover the mechanism of WC’s activity enhancement for Pt-based
ORR catalysts, Professor P.K. Shen et al. [220] used the Gaussian 03 program to